1. Field of the Invention
The present invention relates to an absorption heat pump and a cogeneration system which utilize exhaust heat.
2. Description of the Related Art
An example of a cogeneration system (electric energy-heat simultaneous supply system) is a fuel cell. A fuel cell, for example, a phosphoric acid fuel cell, is a system in which hydrogen gas (H.sub.2) obtained by reforming city gas, etc. and oxygen (O.sub.2) in air are respectively supplied to the cathode and anode that are separated from each other in a solution of phosphoric acid, in this example, so as to generate electric power. At the anode, hydrogen ions (H.sup.+) which have moved from the cathode through the phosphoric acid solution, react with hydroxyl ions (OH.sup.-) generated at the anode. As a result, water (H.sub.2 O) is generated, and heat of reaction is simultaneously generated. It is therefore necessary to cool the cell in order that power generation can be performed continuously. For this purpose, the heat of reaction is normally removed by water cooling. Since such exhaust heat has a temperature level which is not less than 100.degree. C. and which reaches 180.degree. C. as a highest temperature, when a gas-liquid separating apparatus is interposed, it is possible to extract saturated water vapor of 4 to 8 kg/cm.sup.2 G. Hydrogen gas for power generation is obtained, for example, by mixing methane gas (CH.sub.4), the main component of city gas, with a part of the water vapor, and heating the mixture with a burner. Since exhaust gas resulting from combustion by the burner has a high temperature, when such exhaust heat is recovered with cooling water, it is possible to obtain exhaust-heat warm water normally having a temperature of 60.degree. to 85.degree. C.
The total quantity of heat that can be extracted in this way in the form of water vapor and warm water while a fuel cell generates power corresponds approximately to as much as 40% of the quantity of heat which can be obtained through direct combustion of the same amount of city gas (the amount of generated power corresponds approximately to 40% of that fraction). Therefore, it is essential to effectively utilize exhaust heats in order to improve the overall efficiency of the system.
An example of art related to this kind of system is disclosed, for example, in Japanese Patent Unexamined Publication No. 2-37262.
Various forms have been considered for %he utilization of exhaust heat. For example, it has been studied to use exhaust heat as the heat source of absorption-type refrigerators. When extracting warm water from a conventional absorption-type water-cooler/heater, however, it has been impossible to obtain a heat quantity of warm water which is above the input heat quantity, and effective utilization of exhaust heat has not been achieved. No consideration has been given to an exhaust heat processing system which is essential to maintaining the operation of a fuel cell, and no suitable system has been made for enabling exhaust heat of a fuel cell, which is operated in a continuous mode basically, to be applied to certain uses (such as cooling and heating of a predetermined space, and supply of hot-water) which can involve great changes in load. Thus, the problem of how to make a cogeneration system capable of utilizing exhaust heat highly efficiently has not been solved.